Method for cohesively bonding metal to a non-metallic substrate using capacitors

ABSTRACT

A process for cohesive bonding between a metal surface and a nonmetallic substrate is provided. The non-metallic substrate may comprise a plurality of microfilaments and/or nanofilaments dispersed into and below the surface of the substrate. The application of pressure and laterally-oriented high frequency and low amplitude vibration may allow for diffusion bonding between the metal surface and material of the nanofilaments. Another method includes discharging energy from a bank of capacitors to melt adjoining surfaces of the metal surface and nonmetallic substrate. Additionally, a cohesive bonding method may further comprise converting electrical oscillations of ultrasonic frequency into ultrasonic vibrations which are transmitted to the metal body and/or substrate for fusing the two materials together.

RELATED APPLICATIONS

This application is a division of U.S. application Ser. No. 12/045,347now U.S. Pat. No. 8,186,566, filed on Mar. 10, 2008 which claimspriority to U.S. Provisional Application Ser. No. 60/894,213, filed Mar.10, 2007, both of which are hereby incorporated by reference in theirentirety.

BACKGROUND

The present invention relates generally to a method for cohesivelybonding metal to a non-metallic substrate and more particularly, to theuse of metallic micro and nano size filaments, embedded within thenon-metallic material, to create cohesive bonds with the metallicmaterial.

Non-metallic materials, and in particular composite materials such asgraphite-fibers or fiberglass fibers with epoxy matrices, arenotoriously difficult to attach to metallic materials. The most commonlyused methods to create such assemblies are adhesive bonding or the useof fastening devices. Both of these methods have disadvantages relatedto disbonding due to water infiltration and corrosion or due to thefracture of the superficial surfaces where the fastening devices areconnected to the composite material.

Various methods are commonly used to attach two metal surfaces to eachother. Besides fastening, welding is such a method; however, many otherssuch as brazing, soldering, diffusion bonding and adhesive bonding arewidely used in industry. All of these methods are generally dependentupon a plurality of parameters including applied pressure, bondingtemperature, time, and the method of heat application. The surfacefinish of the components can play an important role, as well. To form acohesive bond, it is important for two, clean and flat surfaces to comeinto atomic contact with one another, with microasperities and surfacelayer contaminants being removed from the bonding faces before bonding.

Welding, in general, is making use of high temperatures to melt the twometals in contact with each other or to melt a filler material, creatinga pool of common, molten alloy that when solidified, would stronglyconnect the two together. On the other side, the diffusion bondingprocess is known to create a strong bond between two metals withoutmelting them by using only pressure and lower temperatures, and withoutthe introduction of any extrinsic material.

However, bonding a metal surface to a non-metallic substrate generallycannot be accomplished by any of the methods outlined above and oftenrequires the addition of an extrinsic material, such as an adhesive.Hence, adhesive bonding or fastening methods are extensively used toconnect metallic materials to non-metallic substrates.

Accordingly, it would be desirable to have a bonding method that forms astrong cohesive bond between a metal body and a non-metallic substrate.

SUMMARY OF THE INVENTION

In one aspect of the present invention there is provided a method forcohesive bonding a metal body to a substrate comprising the steps ofcontacting the metal body to a surface of the substrate, the substratecomprising a plurality of microfilaments or nanofilaments dispersed intoor below the surface of the substrate and the metal body surfacecomprising microscopic asperities which contact the plurality ofmicrofilaments or nanofilaments, applying normally-oriented pressure onthe metal body and laterally-oriented high frequency and low amplitudevibrations to the substrate and forming a cohesive bond between themetal body and the substrate.

In another aspect of the present invention there is provided a methodfor cohesive bonding a metal body to a substrate comprising the steps ofcoupling a plurality of capacitors to the metal body and the substrate,contacting the metal body to the substrate, the substrate comprising aplurality of microfilaments or nanofilaments, wherein the microfilamentsor nanofilaments provide microscopic asperities on at least thesubstrate surface which contacts the metal body, discharging energy fromthe plurality of capacitors to raise the temperature of the surfaces ofthe metal body and the substrate which contact one another, applyingpressure on the metal body or substrate and forming a cohesive bondbetween the metal body and the substrate.

In a further aspect of the present invention there is provided a methodfor cohesive bonding a metal body to a substrate comprising the steps ofcontacting the metal body to the substrate, the substrate comprising aplurality of microfilaments or nanofilaments, wherein the microfilamentsor nanofilaments provide microscopic asperities on at least thesubstrate surface which contacts the metal body, positioning a sonotrodeto contact the metal body, applying normally-oriented pressure on themetal body or substrate, vibrating the metal body or substrate andforming a cohesive bond between the metal body and the substrate.

These and other features, aspects and advantages of the presentinvention will become better understood with reference to the followingdrawings, description and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The above-mentioned aspects of the present invention and the manner ofobtaining them will become more apparent and the invention itself willbe better understood by reference to the following description of theembodiments of the invention, taken in conjunction with the accompanyingdrawings, wherein:

FIG. 1 is a schematic of composite material comprising a matrix andfibers having a plurality of microfilaments and/or nanofilamentsembedded in the matrix;

FIG. 2 is a schematic of the composite material of FIG. 1 with a metalbody to be bonded to the matrix;

FIG. 3 is a schematic of the metal body of FIG. 2 being compressed tothe matrix;

FIG. 4 is a schematic of a metal body being bonded to a non-metallicsubstrate via capacitor-discharge bonding;

FIG. 5 is a schematic of a metal body being bonded to a non-metallicsubstrate via localized friction bonding;

FIG. 6 is a schematic of a metal body being bonded to a non-metallicsubstrate via ultrasonic welding; and

FIG. 7 is a schematic showing an enlarged view of the bond formed as theresult of the method of the present invention between a metal surfaceand a substrate comprising microfilaments and/or nanofilaments.

Corresponding reference numerals are used to indicate correspondingparts throughout the several views.

DETAILED DESCRIPTION

The embodiments of the present invention described below are notintended to be exhaustive or to limit the invention to the precise formsdisclosed in the following detailed description. Rather, the embodimentsare chosen and described so that others skilled in the art mayappreciate and understand the principles and practices of the presentinvention.

Broadly the present invention provides methods for cohesively bondingthe surface of a metal body to a non-metallic substrate which maycomprise contacting a metal surface of the metal body with a surface ofthe substrate. The substrate may comprise a plurality of microfilamentsand/or nanofilaments which may provide microscopic asperities on thesurface of the substrate in contact with the metal surface. The methodmay further use a variety of known joining processes such as frictionwelding, capacitor-discharge welding, ultrasonic welding and diffusionbonding to connect the filaments with the metallic body. These methodsmay comprise simultaneously applying normally-oriented pressure to themetal surface and laterally-oriented high frequency and low amplitudevibrations to the substrate and forming a cohesive bond between themetal surface and the substrate. The applied loads are typically belowthose loads which would cause macro-deformation of the components'materials. This process, known as localized friction welding, createslocalized increases of contact temperature that do not exceed 0.5-0.8times the melting point temperature of such materials and thetemperature of the materials can remain in this range for 0.004 secondsto over 3600 seconds depending upon the type of materials being bonded,the joint properties of these materials, and the heating method beingused.

Other joining processes may comprise radiant heating, induction heatingand direct or indirect resistance heating. For example, the diffusionbonding process may be further assisted by additionally exposing thecomponents' materials to higher temperatures, inert gases and/or avacuum. While not wishing to be bound by any particular theory, thecohesive bond may be formed by diffusion of the microfilament and/ornanofilament material into the metal layer, thus forming a stronger bondthan one without the presence of the microfilaments and/ornanofilaments.

An exemplary embodiment of a composite material (hereinafter referred toas “substrate”) is shown in FIG. 1. The substrate 14 comprises a matrixthat may include fibers 18 and a plurality of microfilaments and/ornanofilaments 16 randomly oriented and embedded within the matrix. Themicrofilaments and/or nanofilaments 16 are metallic, but alternativelythey may comprise ceramic, plastic, or any other material known to theskilled artisan. Some or all of the plurality of microfilaments and/ornanofilaments 16 may extend out of a surface 15 of the substrate 14,whereas others may be embedded in the substrate without extending out ofthe substrate.

In one embodiment of the present invention, substrate 14 of FIG. 1 maybe any material desired to form a bond to a metal surface 12 and whichmay have microfilaments and/or nanofilaments 16 dispersed therein. Ingeneral, the substrate 14 comprises non-metallic material. In oneexemplary embodiment, the substrate 14 may comprise a composite materialsuch as, but not limited to, a metal matrix composite, a ceramiccomposite or a polymer composite. The polymer composite may compriseunidirectional or multidirectional oriented fibers of graphite,fiberglass, aramid or a combination thereof. Substrate 14 may compriseany size or form desired. It may be preformed into a desired shape orpart. Alternatively, it may be shaped or formed after bonding to themetal surface.

As described above with reference to FIG. 1, the substrate 14 maycomprise a plurality of microfilaments and/or nanofilaments 16. Theplurality of microfilaments and/or nanofilaments 16 may be dispersed onand/or below a surface 15 (see FIG. 1) of the substrate 14. In oneexemplary embodiment, the plurality of microfilaments and/ornanofilaments 16 are introduced individually into the substrate 14 andmay create an intricate network in the substrate 14. In an alternateembodiment, the plurality of microfilaments and/or nanofilaments 16 maybe introduced into the substrate 14 being physically connected to oneanother, forming a structure such as, but not limited to, a micrometricor nanometric sized foam. It will be appreciated that a network ofmicrofilaments and/or nanofilaments 16 may provide firstly, a strongadhesion bond within the substrate 14 and subsequently provide theopportunity for bonding between metal surface 12 and substrate 14.

In one embodiment of a cohesive bonding process, a metal-bondedsubstrate is shown in FIG. 2. In this process, a metal body 12 may becohesively bonded to the substrate 14 via one of several bondingmethods, three of which will be described below in further detail.Similar to the substrate shown in FIG. 1, the substrate 14 in FIG. 2 maycomprise a plurality of randomly-oriented microfilaments and/ornanofilaments 16 and a plurality of aligned fibers 18 dispersedthroughout substrate 14 and which are usually introduced as a speciallyfabricated cloth.

The microfilaments and/or nanofilaments 16 may form microscopicasperities on the surface 15 of the substrate 14 and may change thematerial characteristics of the substrate 14 at or near the surface 15.The plurality of microfilaments and/or nanofilaments 16 may be dispersedin the substrate 14 during the manufacture of the substrate 14.Alternately, the microfilaments and/or nanofilaments 16 may be dispersedin the substrate 14 afterwards by other methods known in the art. Theplurality of microfilaments and/or nanofilaments 16 may be distributedthroughout the substrate 14 to provide the optimal cohesive bond betweenthe substrate 14 and the surface of the metal body 12. The plurality ofmicrofilaments and/or nanofilaments 16 may be evenly distributedthroughout the substrate 14 or they may be concentrated at the surface15 of the substrate 14 where the surface of the metal body 12 will bebonded, gradually decreasing in the substrate 14 away from the surface15.

In another embodiment of the present invention the microfilaments and/ornanofilaments 16 may comprise a material capable of bonding with themetal body 12. In one exemplary embodiment, the microfilaments and/ornanofilaments 16 may comprise a metal such as, but not limited to,stainless steel or a titanium alloy. In another embodiment, themicrofilaments and/or nanofilaments 16 may comprise a material capableof sustaining the bond or joint between the substrate 14 and the metalbody 12 and may also have desired corrosion resistance as well as littleor no adherent oxide layer.

In one embodiment in which micro or nanofilaments produced using thepresent state of art are embedded in the substrate 14, those filaments16 may have a diameter of less than 100 nm up to 1000 nm incross-sectional dimension. In an exemplary embodiment, nanofilaments 16produced using other, advanced technologies may be less than about 100nm in cross-sectional dimension. It will be appreciated that thecross-sectional dimension of the nanofilaments 16 may be small enough toprovide an optimal number of interactions with the metal body 12 butstill retain integrity and strength. Based on the present technology thenanofilaments 16 may have a length less than about 400 μm. Thenanofilaments 16 may be made by processes known in the art such as, butnot limited to, the process described in U.S. Pat. No. 6,444,256, whichis herein incorporated by reference

In a different embodiment of the present invention, the surface of themetal body 12 may be the surface of a metal strip, a metal sheet, ametal plate or a metal block. It is contemplated that any metal surfacefound on any part or material may be bonded to the substrate 14 usingthe process of the present application. The metal surface 12 maycomprise any metal having the desired properties for the application inwhich the bonded metal and composite complex 10 are to be used. By wayof a non-limiting example, the metal body surface 12 may comprisestainless steel or titanium.

In FIG. 3, a method for cohesive bonding a metal surface 12 to asubstrate 14 is provided. In one embodiment, pressure may be applied ina direction 11 against the metal body 12 such that the metal body 12 iscompressed against the substrate 14. The pressure can be applieduniaxially or isostatically. Uniaxial pressure generally requires lowerpressure in the range of 3-10 MPa to avoid macro-deformation of thebonded materials. Additionally, this process typically requires goodsurface finish on the mating surfaces as the contribution to bondingprovided by plastic yielding is restricted. In general, surface finisheswith roughness values better than 0.4 μm RA and which are free fromcontaminants are advantageous for bonding purposes. As for isostaticpressure, much higher pressures such as 100-200 MPa may be possible andtherefore surface finish is not as critical. For example, surfacefinishes of 0.8 μm or greater may be acceptable for the bonding process.An additional advantage of applying isostatic pressure is that the useof uniform gas pressurization allows complex geometries to be bonded,whereas uniaxial pressure generally can only be used for simple butt orlap joint bonding.

An exemplary method for cohesive bonding is shown in FIG. 4 known ascapacitor-discharge welding. In FIG. 4, a substrate 14 is provided whichincludes fibers 18 and a plurality of microfilaments and/ornanofilaments 16 embedded in the substrate 14. A metal body 12 isbrought into contact with a surface of the substrate 14 such that aportion of the plurality of microfilaments and/or nanofilaments 16 foundon the surface 15 of substrate 14 may contact the metal body 12.Capacitors (not shown) are provided to be coupled to at least one of themetal body 12 and substrate 14 through contact elements 25. Contactelements 25 may be placed onto at least one surface of the metal body 12and/or substrate 14. Energy stored in the capacitors at specificvoltages may be released or discharged through contact elements 25 to 14and 12. As the energy is discharged, an instantaneous arc may be createdwhich melts the adjoining surfaces of the metal body 12 andmicrofilaments and/or nanofilaments 16. Either simultaneously or shortlythereafter, pressure may be applied to both materials such that thematerials compress against one another and a cohesive bond is formedbetween the metal body 12 and microfilaments and/or nanofilaments 16, asthe molten metal solidifies.

The capacitor-discharge welding process is an extremely efficient methodfor welding a wide variety of metals including mild steel, stainlesssteel, aluminium, brass, copper, titanium, and other similar metals. Apowerful bank of capacitors may be provided with each capacitor storingenergy at a specific voltage. The capacitors may range between 450-3000volts. The voltage may depend on the size and material of the componentbeing formed. Large capacitor-discharge welding machines may output 400KA of current and 50 kJ of energy. When energy is discharged, a cohesivebond may be formed in approximately 0.004 seconds or more.

The capacitor-discharge welding process is advantageous for manyreasons. The short welding time localizes the heat and creates weldsadjacent to heat sensitive portions of the material. Thecapacitor-discharge welding process provides excellent bonding with avariety of similar and dissimilar materials without requiring any watercooling, significant power requirements, nor substantial operating costsfor high production rates. This process may be performed in mostenvironments as it does not require large amounts of space and producesvery little, if any, fumes or smoke.

A different cohesive bonding method referred to as localized frictionbonding is shown in FIG. 5. In the embodiment of FIG. 5, the method maycomprise the step of contacting a metal body 12 with a surface 15 of asubstrate 14. The substrate 14 may comprise a plurality ofmicrofilaments and/or nanofilaments 16 dispersed into and below thesurface 15 of the substrate 14. The surface of the metal body 12 mayhave microscopic asperities (not shown) as it will be appreciated mostmetal surfaces are not absolutely smooth. In contacting the metal body12 to the surface 15 of the substrate 14, the microscopic asperities ofthe surface of the metal body 12 may come into contact with themicrofilaments and/or nanofilaments 16 of the substrate 14. Themicrofilaments and/or nanofilaments 16 provide microscopic asperitiesthat aid in the bonding process and may contact the microscopicasperities of the metal body 12.

The method may also comprise the step of simultaneously applyingnormally-oriented pressure 20 on the metal body 12 andlaterally-oriented high frequency and low amplitude vibration 22 to thesubstrate 14 as shown in FIG. 5. The application of the combinedpressure and vibration may produce high temperatures localized betweenthe adjoining surface of the metal body 12 and the microfilaments and/ornanofilaments 16 and may further facilitate metal transfer between themetal body 12 and the material of the microfilaments and/ornanofilaments 16 that is exposed at the surface 15 of the substrate 14.This metal transfer may result in a microcohesive or nanocohesivediffusion bond between the surface of the metal body 12 and themicrofilaments and/or nanofilaments 16.

Friction bonding generally is a solid phase pressure welding processwhere little to no actual melting of the metal body occurs. By rubbingthe adjoining surfaces of the metal body and the substrate together,sufficient heat is produced for creating local plastic zones.Accordingly, two atomically clean metal surfaces may be brought togetherunder pressure and an inter-metallic bond is formed. The correspondingheat may be confined to the interface of the two materials. The heatinput may be low and the amount of work applied to the bonded arearesults in grain refinement.

One advantageous characteristic associated with friction bonding is theability to weld alloys and combinations of alloys which were previouslyregarded as “un-weldable.” With localized friction bonding processes, itis now possible to produce dissimilar metal joints, join steel, copper,and aluminium to themselves and/or to each other, and to successfullyweld alloys.

An alternate cohesive bonding method, ultrasonic welding, is shown inFIG. 6. In the embodiment of FIG. 6, the method may comprise the step ofcontacting a metal body 12 with a surface 15 of a substrate 14. Thesubstrate 14 may comprise a plurality of microfilaments and/ornanofilaments 16 dispersed into and below the surface 15 of thesubstrate 14. The surface of the metal body 12 may have microscopicasperities as it will be appreciated most metal surfaces are notabsolutely smooth. A sonotrode 26 may be positioned to be in contactwith a surface of the metal body 12. Likewise, an anvil 27 may bepositioned against a surface of the substrate 14 and it holds thematerials to be welded statically together. A welding tool (not shown)may attach or couple to the material to be bonded and the tool moves ina longitudinal direction. The metal body 12 and substrate 14 may bepressed together and a generator (not shown) may produce electricaloscillations of ultrasonic frequency. In one embodiment, a transducer(not shown) may convert the electrical oscillations into mechanicalvibration which in turn is transmitted to the sonotrode 26. Thesonotrode transmits the ultrasonic vibrations 28 to the metal body 12and substrate 14. Generally, the sonotrode 26 needs to be mountedtightly to the metal body 12 to avoid friction and other losses. Thesimultaneous action of static and dynamic forces causes the metal body12 and substrate 14 to fuse together without requiring the addition ofan extrinsic material.

For plastic materials, high frequency vertical vibrations are used toincrease the temperature and plasticizes the materials. Vibrations mayreach frequencies of about 20-70 kHz. During ultrasonic metal welding, acomplex process is triggered involving static forces, oscillatingshearing forces, and a moderate temperature increase in the weldingarea. The magnitude of these factors depends on the thickness of thework pieces (viz., the metal body 12 and substrate 14), their surfacestructure, and their mechanical properties. Typical frequencies mayreach 20-40 kHz, which is above the frequency that is audible to a humanear and also permits the best possible use of energy. Generally,ultrasonic welding is used for forming small components that requireless energy such as watches, cassettes, plastic products, toys, medicaltools, and packaging.

In the embodiment of FIG. 7, a resulting component 24 is formed fromcohesive bonding between a metal body 12 and a substrate 14. The metalbody 12 may include microscopic asperities and the substrate may includea plurality of microfilaments and/or nanofilaments 16. Other componentsmay be formed via any of the above-described methods and the type ofcomponent being made should not be limiting.

While exemplary embodiments incorporating the principles of the presentinvention have been disclosed hereinabove, the present invention is notlimited to the disclosed embodiments. Instead, this application isintended to cover any variations, uses, or adaptations of the inventionusing its general principles. Further, this application is intended tocover such departures from the present disclosure as come within knownor customary practice in the art to which this invention pertains andwhich fall within the limits of the appended claims.

1. A method for cohesively bonding a metal body to a substratecomprising the steps of: coupling a plurality of capacitors through aplurality of contact elements to the metal body and the substrate;contacting the metal body to the substrate, the substrate comprising aplurality of microfilaments or nanofilaments, wherein the microfilamentsor nanofilaments provide microscopic asperities on at least a substratesurface which contacts a surface of the metal body; discharging energyfrom the plurality of capacitors to raise the temperature of thesurfaces of the metal body and the substrate which contact one another;applying pressure on the metal body or substrate; and forming a cohesivebond between the metal body and the substrate, wherein the substrate isa material comprising a metal matrix composite, a polymer composite or aceramic composite.
 2. The method of claim 1, wherein the contacting stepoccurs before the coupling step.
 3. The method of claim 1, wherein theapplying pressure step occurs simultaneously with or after thedischarging step.
 4. The method of claim 1, wherein the metal bodyconsists of one of mild steel, stainless steel, aluminum, brass, copper,and titanium.
 5. The method of claim 1, wherein the plurality ofcapacitors store energy at specific voltages dependent upon the size andmaterial of a component being formed.
 6. The method of claim 5, whereinthe plurality of capacitors store energy at voltages between about475-3000 volts.
 7. The method of claim 1, wherein the forming step formsa cohesive bond free from distorting or discoloring.
 8. The method ofclaim 1, further comprising creating an instantaneous arc which meltsadjoining surfaces of the metal body and the substrate.